This invention relates to a high security lock mechanism and, more particularly, to an electronically controlled combination lock and lock-bolt operable by a very small amount of self-generated electrical power.
Items of extremely sensitive nature or very high proprietary value often must be stored securely in a safe or other containment device, with access to the items restricted to selected individuals given a predetermined combination code necessary to enable authorized unlocking thereof. It is essential to ensure against unauthorized unlocking of such safe containers by persons employing conventional safe-cracking techniques or sophisticated equipment for applying electrical or magnetic fields, high mechanical forces, or accelerations intended to manipulate elements of the locking mechanism to thereby open it.
Numerous locking mechanisms are known which employ various combinations of mechanical, electrical and magnetic elements both to ensure against unauthorized operation and to effect cooperative movements among the elements for authorized locking and unlocking operations.
One example of such recently-developed devices is disclosed in U.S. Pat. No. 4,684,945, to Sanderford, Jr., which relates to an electronic lock actuated by a predetermined input through a keyboard outside a safe to a programmable control unit within a housing of the safe. The device has an electric motor for driving a lock-bolt for locking a safe door to the safe housing, and means for displaying codes entered by the user, with a facility for selectively changing the necessary code. The device also has a battery-powered backup circuit maintained in a dormant state to conserve energy until an actuation key is operated. A microprocessor of the unit is programmed to activate a relatively high frequency of power output pulses at the start of movement of a locking bolt by the electric motor, to overcome inertia and any sticking forces on the bolt, and a lower frequency of power pulses to complete the movement of the bolt.
Another example is provided in U.S. Pat. No. 4,674,781, to Reece et al., which discloses an electric door lock actuator and mechanism having manual and electrically driven locking means. This device utilizes a combination of a lost motion coupling and resilient springs for driving a motive means to a neutral position, to thereby isolate an electric motor and gearing from the locking means so that the locking means may be operated manually without back-driving of the electric motor and intermediate gearing.
A major problem with such devices is that they require substantial amounts of electric power to perform their locking and unlocking functions. For securely storing and accessing highly sensitive or valuable items, it is important to avoid depending on the ready availability of sufficient electrical power for driving the locking mechanism. In fact, for many applications, the use of long-life batteries, even to power a small microprocessor, may also be deemed unacceptable.
In short, for high security storage of sensitive or valuable material, in light of the availability of sophisticated computer-assisted means and methods for unauthorized operation of locking mechanisms, there exists a need for an autonomous locking mechanism that does not require batteries or external sources of power for any purpose, receives and recognizes only specific user-selected combination code information for access, emanates no information useful to persons attempting unauthorized operation, and is made to resist unauthorized operation even when subjected to strong externally imposed electrical, magnetic or mechanical forces, and satisfies other U.S. government specifications. Most important, once the mechanism is put in its locked position it loses all xe2x80x9cmemoryxe2x80x9d of the input combination code and requires a totally new and correct provision of the complete combination code to be unlocked again.
The present invention, as more fully disclosed hereinbelow, meets these perceived needs at reasonable cost with a geometrically compact, electrically autonomous, locking mechanism.
It is an object of this invention to provide a locking mechanism which remains securely in a locked state until, following receipt of a predetermined combination code, a very small amount of electrical power is employed to put it in condition to be manually unlocked thereafter.
It is another object of this invention to provide a locking mechanism actuated by the input of a selected combination code followed by the delivery of a very small amount of electrical power generated during input of a user-selected combination code to a low friction engagement means to put the same in a position to enable purely manual unlocking of the mechanism thereafter.
Yet another object of this invention is to provide a locking mechanism which upon being put into a locked state remains in that state immune to electrical, magnetic, thermal or mechanical inputs accompanying attempts at unauthorized unlocking thereof.
It is an even further object of this invention to provide a secure locking mechanism which is unlocked by the provision of a preselected combination code within a specified time followed by the provision of a very small amount of electrical power to move an engagement element to a position to enable solely manual unlocking of the mechanism thereafter.
It is an even further object of this invention to provide a locking mechanism which utilizes a very small amount of electrical power, generated during input of a user-provided combination code, to be put into condition for manual unlocking, the mechanism, upon being manually put into a locked state, remaining in such a locked state until a predetermined combination code is entered.
These and other related objects are realized, according to a preferred embodiment of the invention, by providing a locking mechanism which comprises a first means for moving an engagement element from a disengaged position to an engageable position thereof solely upon receipt of a controlled predetermined electrical power output, a manually operated second means for engaging the engagement element when the latter is in its engageable position for thereby manually moving the first means further in a first direction and back in a second direction, and third means for driving a lock-bolt engaged by the further movement of the first means to drive the lock-bolt to locking and unlocking positions thereof in correspondence with movements of the first means in the first and second directions respectively. Movement of the first means in the second direction restores security by returning the engagement element to its disengaged position when the lock-bolt reaches its locked position.
In still another aspect of the invention, the first means comprises an electrical stepper motor having a rotor supporting the engagement element and having stable positions determined by magnetic detents which correspond to the disengaged and engageable positions of the engagement element.